Dielectric glasses

ABSTRACT

A family of dielectric glasses having properties such that, when heat is applied to seal the dielectric glasses, there is no crazing in a MgO overcoat. These dielectric glasses have such viscosity properties as not to craze a MgO overcoat at a temperature of about 480*C corresponding approximately to log viscosity of 10.3 poises and yet fire into good dielectric films at about 610*C. The glass has substantially the following constitutents:

United States Patent [191 Brownlow et al.

[ DIELECTRIC GLASSES [75] inventors: James M. Brownlow, Crompond;

Relva C. Buchanan, Fishkill; R20 R. Tumrnala, Wappingers Falls, all of N.Y.

[73] Assignee: International Business Machines Corporation, Annonk, NY.

[22] Filed: Dec. 6, 1973 211 App]. No.: 422,378

[52] US. Cl 106/53; 106/49 [Sl] Int. Cl.*.... C03C 3/10; C03C 3/04; C03C 5/02 [58] Field of Search 106/53, 49; 252/518 [56] References Cited UNITED STATES PATENTS 3,238,15l 3/l966 Kim 106/53 Dec. 23, 1975 Primary Examiner-Winston A. Douglas Assistant Examiner-Mark Bell Attorney, Agent, or Firm-Edward S. Gershuny [57] ABSTRACT A family of dielectric glasses having properties such that, when heat is applied to seal the dielectric glasses, there is no crazing in a MgO overcoat. These dielectric glasses have such viscosity properties as not to craze a MgO overcoat at a temperature of about 480C corresponding approximately to log viscosity of [0.3 poises and yet tire into good dielectric films at about 6l0C. The glass has substantially the following constitutents:

a, b Wei m lbO ss.o s1.o sio, |2.o-|4.o n.0, 21.0410

1-212 CaO 210-515 Nap 1.3-2.2

5 Claims, No Drawings DIEELECTRIC CLASSES BACKGROUND OF THE lNVENTlON This invention relates to a composition of dielectric glasses. More particularly, the invention relates to novel glasses which are particularly suited for use in the manufacture of gas panel displays.

Plates used in manufacturing a gas display panel contain a dielectric layer with a magnesium oxideovercoat. lo the prior art, during the step of sealing plates together, the magnesium oxide overcoat layer has a tendency to craze (develop small cracks). This is,- of course, undesirable as the underlying dielectric is then exposed to gas plasma.

It is a primary object of this invention to provide a dielectric glass having such properties that the crazing temperature will be higher than the temperature used for sealing panels together and that substantially flat, warp-free panels can be produced.

Additional objects of the invention are to provide a dielectric glass having the following properties:

a steep viscosity-temperature curve such that the dielectric is capable of being fired at a temperature below the incipient fusion temperature of the glass substrate;

a thermal co-efficient of expansion (TCE) which matches that of the substrate;

capable of being flowed easily into bubble free films with little or no tendency to crystallize; and

good chemical durability.

SUMMARY OF THE INVENTION The above and other objects are achieved in accordance with the invention by providing a dielectric glass composed substantiallyof the following constituents:

k b wei ht PbO 55.5-57.0 SiO, l2.0-l4.0 5,0, 2l.0-22.0 n.0, 1.0-4.0 M30 1.5-2.2 CaO 2.0-5.5 Nr O Lil-2.2

When the dielectric glass of this invention is used in the process of manufacturing a gas display panel, the glass substrate upon which it is deposited is typically a sodalime-silica float glass having a thermal co-efficient of expansion (TCE) of approximately 94x10" per C to the set point of the dielectric (approximately 430C). Therefore, the dielectric glass should preferably have a TCE of approximately 90-98 to its set point. This corresponds to a TCE of approximately 78-86 in the tem erature range from room temperature (approximately 22C) to 300C. Glasses which are particularly suitable for use in this process consist of substantially the following constituents:

PbO

I: b weight 56. 56.7

The primary advantage of this invention is that, when using the dielectric glasses described herein a magnesium oxide overcoat layer will not craze unless it is subjected to a relatively high temperature. This is of particular advantage in vitreous sealing technology using glass rod preforms. Referring particularly to glasses whose constituents are within the preferred ranges described above, the crazing temperature (480C and above) is higher than the temperature normally used to seal glass plates together (around 470-480C) using vitreous sealing glasses during the processof manufacturing a gas display panel.

. Additionally, each of the glasses described herein also exhibits one or more of the following desirable properties:

it can be fired below the incipient fusion temperature 1 of the substrate;

its TCE is fairly close to that of the substrate;

it flows easily into a smooth bubble free film with little or no tendency to crystallize; and

it has good chemical durability.

The foregoing and other objects, features and advantages of the invention will be apparent from the following more particular description of preferred embodiments thereof.

DETAILED DESCRIPTION giving higher crazing temperatures, glasses with more than about 3 per cent MgO tend to show fine crystals in the tired dielectric. Glasses with higher CaO contennt (above about 5.5 per cent) also give higher crazing temperatures but they tend to have higher TCEs.

by weight PbO 55.5-56.7 SiO, 12.0-1 3.5 8,0; 2 I .0-2 I .5

i238 CaO 2.0-5.5 Nap l .8-2.2

EXAMPLES l-IV Examples l-lV are four dielectric glass compositions which are particularly suitable for use in fabricating gas display panels, especially when using a glass substrate which has a TCE equal to 89. (When thermal co-efficients of expansion are given herein, they are expressed in units multiplied by l0"/C and refer to the temperature range from room temperatureto 300C.)

Percent By Weight I II III IV PbO 56.0 56.7 56.0 56.0 SiO, 12.0 l2.0 l2.5 l2.5 8,0 l.S 2l.0 21.5 21.5 M 0, L0 2.8 2.0 L0 MgO 2.0 2.0 2.0 2.0

3 i Percent By Weight-continued i II III IV CaO V 5.5 3.5 4.0 5.0 Na,() 2.0 2.0 2.0 2.0 TCE( RT-300) 86 84 83.9 85

above about above about TCraze 480 480 480 480 within the following ranges.

G: by weight lbO 56.0-56.7 SiO, 12.0-l2.5 8,0, 2| .0-2l.5 ,0, |.o-2.s MgO [3-2.2 C10 3.5-5.5 N50 l.8-2.2

EXAMPLES V-Vlll Examples V-VIII are four additional dielectric glasses which offer various advantages.

Percent By Weight V Vi VII VIII FbO 56.0 55.0 55.5 57.0 SiO,- l3.0 12.5 l3.5 l4.0 8,0, 21.0 2L0 2L0 22.0 n.0, 3.0 4.0 2.0 L MgO 2.0 L 2.0 2.0 C1D 3.0 4.0 4.0 2.0 Na) 2.0 2.0 2.0 2.0 TC (RT-300) so no.9 1s s2 The glasses of examples V-Vlll are somewhat less desirable than examples l-lV for use in the preferred process of manufacturing gas panel displays primarily because they have lower 8,0,!Si0, ratios and are therefore harder to make bubble-free. However, examples V-Vlll could be of substantial value in processes where they can be fired at slightly higher temperatures. Examples l-Vlll comprise a class of dielectric glasses constituted substantially as follows.

b wei ht I 55.0-57.0

PbO

SiO, l2.0-l4.0 a o. 21.0-22.0 Alp, 1.0-4.0 mo 1.5 2.2 CsO 2.0-5.5 M rs-2.2

ADDlTlONAL CONSIDERATIONS Although glasses which have a high SiO, content (for example, l5 per cent or more) have higher crazing temperatures, they cannot be conveniently flowed into smooth bubble free dielectric films due to their shallow viscosity-temperature relationship. For a given crazing temperature, a glass with a higher 8,0, content than SiO, can be flowed more easily in oxidizing atmospheres (in all of the examples given above the 13,0, content is higher than the SiO, content). However, prior art glasses that are high in 8,0, content typically have low crazing temperatures and low chemical durabilities.

As is described in copending application Ser. No. 374,189 filed June 27, I973, the MgO-crazing temperature in high 8,0, glasses can be increased by incorporating MgO, CaO or (preferably) both into the glass composition. These glasses can be fired into smooth bubble free films because they have a steep viscositytemperature relationship.

An essential element of the glasses described herein is the inclusion of Na,(), preferably in concentrations between approximately l.8 annd 2.2 percent, in order to minimize detrimental leaching of sodium from alkali containing substrates during reflow of the dielectric glass. Such leaching could cause substrate deformation.

it should also be noted that these glasses respond to wet air and wet oxygen firing resulting in the use of lower firing temperatures for the same crazing temperature. For example, both Glass I described herein and a glass consisting of 7L5 per cent PhD, 6 per cent 8,0,, 17 per cent SiO, and 5.5 per cent alumina would have approximately the same MgO crazing temperature, the latter cannot be fired bubble-free below about 660C, which is too high for the substrate. it is important that the glasses can be fired in a wet atmosphere as this causes in situ passivation of the CrlCu/Cr metallurgy.

While the invention has been particularly shwon and described with reference to preferred embodiments thereof, it will be understood by those skilled in the art that the above and other changes in form and details may be made therein without departing from the spirit and scope 6f the invention.

What is claimed is: a w

l. A dielectric glass'having a thermal coefficient of expansion (from room temperature to 300C) in the range of approximately 83.9-86.0 X 10" per C and a crazing temperature with respect to a magnesium oxide overcoat above about 480C, consisting essentially of the following ingredients in the following proportions:

Percent by weight Lead oxide (PbO) Boric oxide 0,) 2l.0-2l.5 Silicon oxide l0,) lZ.0-l 2.5 Alumina (A Lil-2.8 slcium osi e (CaO) 3.5-5.5

nesiurn oxide (MgO) 2.0 turn oxide (Na O) 2.0.

6 -9 P 2L5 Percent 2 Pement 56.0 percent PbO, 21.5 percent 8,0,, l2.5 percent percent pemem pep SiO,, [.0 percent AI,O 5.0 percent CaO, 2.0 percent Mgo and 2.0 percent M1 0. 5. A dielectric glass in accordance with claim 1 consisting essentially of:

cent MgO and 2.0 percent Na,(}. 

1. A DIELECTRIC GLASS HAVING A THERMAL COEFFICIENT OF EXPANSION (FROM ROOM TEMPERATURE TO 300*C) IN THE RANGE OF APPROXIMATELY 83.9-86.0 X 10**-7 PER *C AND A CRAZING TEMPERATURE WITH RESPECT TO A MANGANESE OXIDE OVERCOAT ABOVE ABOUT 480*C, CONSISTING ESSENTIALLY OF THE FOLLOWING INGREDIENTS IN THE FOLLOWING PROPORTIONS:
 2. A dielectric glass in accordance with claim 1 consisting essentially of: 56.0 percent PbO, 21.5 percent B2O3, 12.0 percent SiO2, 1.0 percent Al2O3, 5.5 percent CaO, 2.0 percent MgO and 2.0 percent Na2O.
 3. A dielectric glass in accordance with claim 1 consisting essentially of: 56.7 percent PbO, 21.0 percent B2O3, 12.0 percent SiO2, 2.8 percent Al2O3, 3.5 percent CaO, 2.0 percent MgO and 2.0 percent Na2O.
 4. A dielectric glass in accordance with claim 1 consisting essentially of: 56.0 percent PbO, 21.5 percent B2O3, 12.5 percent SiO2, 2.0 percent Al2O3, 4.0 percent CaO, 2.0 percent Mgo and 2.0 percent Na2O.
 5. A dielectric glass in accordance with claim 1 consisting essentially of: 56.0 percent PbO, 21.5 percent B2O3, 12.5 percent SiO2, 1.0 percent Al2O3, 5.0 percent CaO, 2.0 percent MgO and 2.0 percent Na2O. 